On Aug 10, 10:57 pm, Michael Black wrote:
On Sun, 10 Aug 2008, raypsi wrote:
I guess what I really wanted to do is make a PA
for all bands with a plug in PCB. That would have
the right size coils etched into it for each band.
So when I change bands I would just unplug one
band PCB and plug in another PCB for the band
I want. Rather than a band switch that would arc
out. Or a roller inductor that I would have to turn
to the right number of turns to get to the band I
want. Alot cheaper to plug in PCB's than the
price of a band switch with lots of wires
or roller inductor.
This would eliminate trouble switching to 10
meters with a band switch I suspect.

I'd use an edge card connector to plug the coils/PCB
into and out of an edge connector.

Well you wouldn't be changing bands with the transmitter
going. So in that regard, plug-in coils, bandswitch or
jumpers are about the same.

People like switches so they don't have to turn off their
transmitter (to ensure not dangerous voltages) reach into their
transmitter and plug in coils. If you have to reach in,
at least some of the other possibilities are viable.

Your edge connector may introduce problems of bad contacts.
If you have to run current through them, bad contacts will
not be a good thing.

And I'd add that a large inductor may not be feasible etched
on a circuit board. The only times I've seen coils etched
into circuit board have been when the coils are low inductance,
the sort of values you'd see at VHF and UHF. Making a coil
large enough may result in way too big a plugin board.

You haven't really specified, I don't think, whether this
is a tube or transistor transmitter. In the days of tubes,
the transmitters were narrow band. With transistors, they've
generally been broad band. So with transistor transmitters,
the bandwitching has been about switching in bandpass or low
pass filters for each band, and since the broadband transmitter
has 50ohm output impedance, the switching is relatively easy.

Michael VE2BVW

Yes it's a tube PA I bought a 4-1000A from ebay
there isn't much current at 6000 volts at least not for
Ham Radio power. there's a variety of ways to power down the
PA as soon as I start to pull the PCB out before it becomes
disconnected. And to soft start it up as I'm plugging another
PCB coil in.

The inductance is more dependent on the diameter of the coil
and the number turns on the coil. So a 6 inch square PCB
with a 6 inch diameter 10 turn coil etched on it would
work 160 meter band. Or at least it has enough inductance
to operate on the 160 meter band.

I've seen too many of a senior moment when they hot switch
a band switch or when parasitics build up from a shorted
parasitic resistor and the VHF RF goes to that band switch
looking for a path to ground blowing it to kingdom come.

73
n8zu

raypsi wrote:
On Aug 10, 10:57 pm, Michael Black wrote:

On Sun, 10 Aug 2008, raypsi wrote:

I guess what I really wanted to do is make a PA
for all bands with a plug in PCB. That would have
the right size coils etched into it for each band.
So when I change bands I would just unplug one
band PCB and plug in another PCB for the band
I want. Rather than a band switch that would arc
out. Or a roller inductor that I would have to turn
to the right number of turns to get to the band I
want. Alot cheaper to plug in PCB's than the
price of a band switch with lots of wires
or roller inductor.
This would eliminate trouble switching to 10
meters with a band switch I suspect.

I'd use an edge card connector to plug the coils/PCB
into and out of an edge connector.

Well you wouldn't be changing bands with the transmitter
going. So in that regard, plug-in coils, bandswitch or
jumpers are about the same.

People like switches so they don't have to turn off their
transmitter (to ensure not dangerous voltages) reach into their
transmitter and plug in coils. If you have to reach in,
at least some of the other possibilities are viable.

Your edge connector may introduce problems of bad contacts.
If you have to run current through them, bad contacts will
not be a good thing.

And I'd add that a large inductor may not be feasible etched
on a circuit board. The only times I've seen coils etched
into circuit board have been when the coils are low inductance,
the sort of values you'd see at VHF and UHF. Making a coil
large enough may result in way too big a plugin board.

You haven't really specified, I don't think, whether this
is a tube or transistor transmitter. In the days of tubes,
the transmitters were narrow band. With transistors, they've
generally been broad band. So with transistor transmitters,
the bandwitching has been about switching in bandpass or low
pass filters for each band, and since the broadband transmitter
has 50ohm output impedance, the switching is relatively easy.

Michael VE2BVW


Yes it's a tube PA I bought a 4-1000A from ebay
there isn't much current at 6000 volts at least not for
Ham Radio power. there's a variety of ways to power down the
PA as soon as I start to pull the PCB out before it becomes
disconnected. And to soft start it up as I'm plugging another
PCB coil in.

The inductance is more dependent on the diameter of the coil
and the number turns on the coil. So a 6 inch square PCB
with a 6 inch diameter 10 turn coil etched on it would
work 160 meter band. Or at least it has enough inductance
to operate on the 160 meter band.

I've seen too many of a senior moment when they hot switch
a band switch or when parasitics build up from a shorted
parasitic resistor and the VHF RF goes to that band switch
looking for a path to ground blowing it to kingdom come.

73
n8zu

Gosh! I thought I was the only one left making pancake coils.
Of course mine were for my little 30watt rotary spark gap TX.
Its one I use at NZVRS exhibitions to show visitors what spark
stations looked like. The "ring of fire" effect always fascinates them.
In the case of Tesla and spark gear generally the fact that the 2 ends
of the winding were widely separated was very important as the peak
voltages were so high.
It would be intersting to here if you idea pans out.
73 Cliff Wright ZL1BDA ex G3NIA